The present invention relates to an electrode structure and to an electric heater provided with the electrode. More specifically, the present invention relates to an electrode structure for electrifying, for example, a subject installed in a metallic housing and to an electric heater provided with the electrode structure.
In the catalytic converter used for purifying an exhaust gas of automobiles, etc., there has been known a technique to mount an electric heater on a catalytic converter so as to raise a temperature of a catalyst up to a working temperature in the early stage. The electric heater generally has a structure that a metallic honeycomb structure is installed and held in a metallic housing such as a can and that the honeycomb structure to be electrified is provided with an electrode for electrification.
As an electrode structure for such an electric heater, there has conventionally been proposed an electrode structure shown in FIG. 10. In FIG. 10, the electrode structure has an electrode 6 made of a metallic bolt. To the metallic bolt 6 are fixed insulating members (insulators) 8 and 8' and a jig 26 for fixing the insulators via a washer 10 by means of a nut 14. The insulating members insulate a metallic housing (can) 2 from the electrode 6. The electrode structure is inserted to a throughhole 12 arranged in the metallic housing 2 and fixed to the metallic housing by welding. One end of the electrode 6 inside the metallic housing 2 is connected with a part of a honeycomb structure 4 by means of a connecting member 16. Additionally, a gas sealability is maintained by a cement sealing material 28.
In an electric heater provided with such an electrode structure, the electrode structure preferably contains a lead wire in view of easy mounting on an exhaust gas pipe of automobiles, etc., one end of the lead wire being unitarily mounted on the electrode structure for convenience of composing. In this case, there sometimes happens that water splashes the electrode during driving a car, for example, in a rain, thereby causing an electric short, corrosion, etc., which require to be avoided.
An electric heater preferably has a small size in view of a space where the heater is fixed so as to actually use for an exhaust gas pipe of automobiles, etc. Particularly, a length of an electrode is preferably as short as possible. When a length of an electrode is shortened, it is required to consider inconvenience such as deterioration of a coat covering a lead wire because a temperature of an end portion of the electrode rises up, workability upon composing the electrode, and the like, when the length of the electrode is simply shortened.
Further, this electrode structure is required to ensure that a gas sealability is maintained and that the metallic housing is insulated from the electrode.